The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed.
For example, lithography is a technique frequently used in IC manufacturing for transferring IC designs to a semiconductor substrate. A typical lithography process includes coating a resist (or photo resist) over a substrate, exposing the resist to a radiation such as deep ultraviolet (DUV) ray or extreme ultraviolet (EUV) ray, and developing and partially stripping the resist to leave a patterned resist over the substrate. The patterned resist is then used in subsequent etching processes in forming ICs. During such etching processes, some characteristics of the patterned resist, such as critical dimension (CD), line width roughness (LWR), and line edge roughness (LER), may be transferred to final IC features such as transistor gates. With the decrease of the IC device dimensions, the CD, LWR, and/or LER of transistor gates (as well as other IC features) are being recognized as major concerns. Accordingly, advancement in lithography process is generally desirable to meet the demand of the continued semiconductor miniaturization.